The main focus of this inter-disciplinary Project is on the biotransformation and pharmacodynamics of opioid and related neuropeptides (e.g., the dynorphins and beta-endorphin), as they underlie these neuropeptides' ability to modulate dopaminergic function or cocaine effects under normal conditions or in addictive states. Four related hypotheses will be tested, in order to systematically investigate the pharmacodynamics and biotransformation of opioid neuropeptides in vivo, in rodents (using microdialysis and place preference assays), in non-human primates and in humans, using a neuroendocrine assay (prolactin levels; a quantitative biomarker of kappa- and mu-opioid effects, also a model system to test the modulatory effects of opioids on a dopaminergic system). Hypothesis #1: There is differential biotransformation of these neuropeptides in different rodent brain areas, in primate blood and CSF, and in human blood. It is therefore proposed to apply novel mass spectrometry techniques to provide quantitative information on the biotransformation of endogenous opioid neuropeptides in these systems. Hypothesis #2: The opioid neuropeptides act similarly to selective, high-efficacy non-peptidic opioid agonists in their modulation of dopaminergic function and cocaine-induced effects in vivo, including cocaine-induced reinforcement as reflected in a place preference paradigm. It is therefore proposed to determine the pharmacodynamics (potency, apparent efficacy and receptor selectivity) of the opioid neuropeptides in microdialysis and place preference assays in rodents, following local administration, Hypothesis #3: The opioid neuropeptides may be selective high-efficacy opioid agonists in primates, but their ability to cause functional changes following repeated administration may differ from that of non-peptidic opioid agonists. It is therefore proposed to determine the pharmacodynamics of these neuropeptides on prolactin levels, a neuroendocrine biomarker. Hypothesis #4: Dynorphin and beta-endorphin will differ in their pharmacodynamic profile in normal volunteers vs. patients in addictive diseases in the above neuroendocrine biomarker. These differences may reflect changes in endogenous opioid systems related to the patients' addictive status. The overall aim of this project is to provide an integrated, quantitative analysis of in vivo pharmacodynamics of opioid peptides and their modulation of dopaminergic function and cocaine effects.